An electronic circuit board having a circuit pattern comprising a metal or an insulating material in a thin film form on a substrate has hitherto been used for computers, communications, information home appliances, various display devices and the like.
Then, in order to respond to the rapidly developing high-level information society, this electronic circuit board is required to realize higher integration (higher definition) and larger area.
For forming this circuit pattern, there has been generally employed a method using a photolithography etching process. A typical process of this method is illustrated in FIGS. 9 and 10.
Here, FIG. 9 illustrates a part of conventional steps of forming a circuit pattern, in which (a) to (e) are each a cross-sectional view illustrating a diagrammatic configuration of an electronic circuit board; and FIG. 10 illustrates the continuation of the steps of FIG. 9, in which (f) to (j) are each a cross-sectional view illustrating a diagrammatic configuration of an electronic circuit board.
As illustrated in FIGS. 9 and 10, in this method, a thin film for forming a circuit pattern is formed on the entire or partial surface of a substrate, and a resist is then coated and dried to form a resist layer. Then, the resist layer is exposed through a mask and developed, thereby forming a reverse pattern (reverse circuit pattern) to the circuit pattern. Thereafter, a desired circuit pattern is formed through etching and removal of a resist layer. This method is excellent in view of mass productivity because the formation precision of the pattern is good, the same pattern can be reproduced over and over, and plural circuit patterns can be formed on the same substrate.
However, as illustrated in FIGS. 9 and 10, in this method using a photolithography etching process, a number of steps are repeated to complete the circuit pattern. Specifically, in the method as illustrated in FIGS. 9 and 10, after forming a metal thin film 51 on a substrate 50, a resist layer 52 is formed; exposure, development treatment, etching and peeling-off of the resist layer 52 are performed; and furthermore, after forming an insulating layer 53, formation of a resist layer 54, exposure, development, etching and peeling-off of the resist layer 54 are performed.
As described previously, this method requires a very large number of steps including about 22 steps comprising film formation, resist coating, drying, exposure, development, etching, peeling-off of resist layer and the like at every time of forming a circuit pattern comprising a metal thin film and an insulating layer. For that reason, there was involved a problem that the production costs are very high.
Also, in this method, a large amount of a liquid developer, a chemical liquid such as an etching agent and a rinsing liquid are used at every time of the foregoing large number of steps. This involved a problem that not only the yield is low, and the production costs are very high, but environmental loads such as a liquid-waste treatment which has become recently a matter of concern are very large.
Furthermore, etching with an etching agent, etc. was difficult depending upon the kind of a material to be used for a metal oxide film or the like. In consequence, only limited materials having excellent etching properties could be applied in the photolithography etching process.
As conventional methods for coping with these various problems, there is, for example, a patterning method using laser light described in Patent Documents 1 and 2 as shown below.
For the purposes of making a thin film circuit pattern fine and shortening and simplifying a process by surely achieving patterning without using a wet process, Patent Document 1 describes a method for forming a thin film pattern, which is characterized by pattern forming a stencil on the surface of a substrate, subsequently depositing a thin film to be fabricated on the stencil, irradiating energy beams from the back surface side of the substrate and peeling off the stencil, thereby achieving patterning of the thin film.
Also, for the purpose of developing a resist film, peeling off the residual resist and processing a metal thin film, a semiconductor film or an insulating thin film in a completely dry process, Patent Document 2 describes a process for producing a liquid crystal display device, which is characterized by coating a resist film constituted of a polymer material having a urethane bond and/or a urea bond on a glass substrate having a thin film of a metal film, dielectric insulating film or semiconductor film for configuring a liquid crystal display device, or a multilayered film in which a part of the thin film is formed in a pattern form, fabricated thereon; irradiating an excimer laser through a mask having a prescribed opening pattern; removing the resist film in the irradiated portion by an ablation phenomenon to form a resist film pattern in which the thin film is exposed corresponding to the opening pattern of the mask; removing the exposed thin film by the resist pattern through an etching treatment; and then irradiating an excimer laser to remove the residual resist film by an ablation phenomenon.
Now, the patterning method using laser light as in Patent Documents 1 and 2 includes several types. From the viewpoints of environment, costs and the like, a laser patterning method in which laser light is directly irradiated on a thin film formed on a substrate through a photomask, and a part of the thin film is removed to form a pattern on the substrate is preferable. Such a method is also called a direct patterning method.
Furthermore, in this direct patterning method, according to a laser patterning method by stepwise irradiation, it is possible to achieve micro patterning so that a circuit with higher integration (higher definition) can be formed, and a small mask can be used. Therefore, this method is excellent in view of costs and preferable.
The laser patterning method by stepwise irradiation as referred to herein is a sort of the direction patterning method and is a method for irradiating with laser light while moving stepwise a substrate having a thin film formed thereon, thereby achieving laser patterning in a manner the same as in a stepwise exposure method which has hitherto been favorably employed in an exposure step in a circuit pattern forming method.
As conventional methods related to such a laser patterning method by stepwise irradiation, for example, a plasma display panel and a process for producing the same described in Patent Document 3 are exemplified.
Patent Document 3 describes a plasma display panel having a front substrate and a back substrate disposed at prescribed intervals substantially in parallel to the front substrate are provided; plural first electrodes extending in a first direction provided in parallel on the back surface of the front substrate opposing to the back substrate; plural second electrodes extending in a second direction orthogonal to the first direction provided on the front surface of the back substrate opposing to the front substrate; a partition between the adjacent second electrodes to each other; and a fluorescent body between the adjacent second electrodes to each other, wherein the first electrodes are formed by first providing a thin film for the first electrode on the substrate and subsequently irradiating laser beams to be periodically emitted on the thin film continuously in the first direction and at prescribed intervals in the second direction, thereby remaining the thin film between linear laser beam irradiation areas; the laser beams are irradiated such that an arbitrary irradiation area on the thin film to be irradiated with laser beams partly overlaps with a next irradiation area on the thin film to be irradiated with laser beams; and the front substrate and the back substrate are stuck such that when the plasma display panel is viewed from its front, this overlap part between the irradiation areas comes into line with the partition, and a process for producing the same.
When a circuit pattern is formed on a glass substrate by the laser patterning method by stepwise irradiation as described in Patent Document 3 in place of the foregoing photolithography etching process, there may be the case where an overlap portion existing on the glass substrate and doubly irradiated with laser light of the stepwise irradiation causes denaturation to become defective, or the case where it becomes defective due to redeposition of a substance vaporized by laser irradiation light or the like. Such a laser irradiation defect reduces the quality of the glass substrate having a circuit pattern. For example, when this is used as a glass substrate for plasma display, a visible light transmittance of the laser irradiation defective portion differs from that in other portions, thereby adversely influencing the display of a screen.
Patent Document 1: JP-A-6-13356
Patent Document 2: JP-A-10-20509
Patent Document 3: JP-A-2000-348611